Process for manufacture of trichlorotrifluoroethanes

ABSTRACT

This invention relates to a process for the manufacture of C 2  Cl 3  F 3  reaction product from a mixture of C 2  Cl 4  F 2  isomers, and more particularly to the manufacture of C 2  Cl 3  F 3  reaction product which is substantially free of CClF 2  CClF 2 .

BACKGROUND

Tetrachlorodifluoroethanes are readily converted to trichlorotrifluoroethanes (C₂ Cl₃ F₃) by using conventional fluorination. The C₂ Cl₃ F₃ product typically contains greater than 98% of the more symmetrical isomer, CCl₂ FCClF₂ (CFC-113). CFC-113 can be readily isomerized to its more unsymmetrical isomer, CCl₃ CF₃ (CFC-113a) using aluminum trihalide catalyst. CFC-113a can in turn be converted to 1,1-dichlorotetrafluoroethane (i.e., CCl₂ FCF₃ or CFC-114a) by conventional fluorination. CCl₂ FCF₃ is of interest as an intermediate to 1,1,1,2-tetrafluoroethane (i.e., CF₃ CH₂ F or HFC-134a) which can be obtained via catalytic hydrogenolysis of its carbon-chlorine bonds using a supported metal hydrogenation catalyst (see e.g., C. Gervasutti et al., J. Fluorine Chem., 1981/82, 19, pgs. 1-20). HFC-134a is an environmentally acceptable potential replacement for chlorofluorocarbon (i.e., CFC) refrigerants, blowing agents, aerosol propellants and sterilants that are being viewed with concern in connection with the destruction of stratospheric ozone. It is highly desired that the 1,1-dichlorotetrafluoroethane employed in the hydrogenolysis route to HFC-134a has as low a content of 1,2-dichlorotetrafluoroethane (i.e., CClF₂ CClF₂ or CFC-114) as practicable since the presence of CFC-114 during hydrogenolysis can lead to formation of 1,1,2,2-tetrafluoroethane (i.e., CHF₂ CHF₂ or HFC-134; see e.g., J. L. Bitner et al., U.S. Dep. Comm. Off. Tech. Serv. Rep. 136732, (1958), p. 25). HFC-134 mixed in HFC-134a may be objectionable for some applications depending on concentration and, since the two isomers boil only 7° C. apart, separation of the isomers in high purity is difficult.

There remains a need for processes which facilitate the production of CFC-114a substantially free of its isomer, particularly processes which may employ conventional vapor-phase fluorination techniques. This includes processes for producing trichlorotrifluoroethane without producing 1,2-dichlorotetrafluoroethane.

SUMMARY OF THE INVENTION

A process is provided in accordance with this invention for producing a reaction product comprising C₂ Cl₃ F₃ substantially free of 1,2-dichlorotetrafluoroethane. The process comprises the steps of (i) contacting a feed mixture consisting essentially of compounds of the formula C₂ Cl_(4-x) F_(2+x) (where x is 0 or 1) wherein the C₂ Cl₄ F₂ content is between about 10 mole percent and 90 mole percent of said C₂ Cl_(4-x) F_(2+x) and wherein the mole ratio of the total amount of CCl₂ FCCl₂ F and CCl₂ FCClF₂ (i.e., the more symmetric C₂ Cl_(4-x) F_(2+x) isomers) to the total amount of CCl₃ CClF₂ and CCl₃ CF₃ (i.e., the more unsymmetric C₂ Cl_(4-x) F_(2+x) isomers) is at least about 1:9, with an isomerization catalyst to produce isomerization product wherein there is less than about 50,000 parts by weight total CCl₂ FCCl₂ F and CCl₂ FCClF₂ per million parts by weight total of CCl₃ CClF₂ and CCl₃ CF₃ ; (ii) contacting the isomerization product with HF in the vapor phase in the presence of a fluorination catalyst comprising trivalent chromium at an elevated temperature below 400° C. selected to provide a fluorination product containing C₂ Cl₂ F₄, C₂ Cl₃ F₃ and between about 10 and 90 percent of the C₂ Cl₄ F₂ from the isomerization product, wherein the ratio of CCl₂ FCCl₂ F to CCl₃ CClF₂ and the ratio of CCl₂ FCClF₂ to CCl₃ CF₃ are both greater than the ratios thereof in the isomerization product and wherein the molar ratio of CClF₂ CClF₂ to CCl₂ FCClF₂ is less than about 1:9; (iii) recovering the C₂ Cl₂ F₄ and a first portion of the C₂ Cl₃ F₃ from the fluorination product; and (iv) recycling C₂ Cl₄ F₂ and a second portion of the C₂ Cl₃ F₃ from the fluorination product to step (i) along with an additional amount of CCl₂ FCCl₂ F which is at least equal to the amount of C₂ Cl₂ F₄ and C₂ Cl₃ F₃ recovered in step (iii) and is sufficient to provide said feed mixture ratio of C₂ Cl₄ F₂ to C₂ Cl_(4-x) F_(2+x).

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of an embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The process of this invention involves the vapor-phase catalytic fluorination of a mixture of tetrachlorodifluoroethane isomers. CCl₂ FCClF₂ reaction product substantially free of CClF₂ CClF₂ is produced. The C₂ Cl₄ F₂ is present in the mixture of halogenated hydrocarbons used in the fluorination step in a molar ratio of CFC-112 to CFC-112a from about 19:1 to 1:19. Preferably, the ratio of CFC-112 to CFC-112a is less than about 1:1, and more preferably is less than about 1:9. In accordance with this invention, the fluorination is under conditions where there is no substantial production of CClF₂ CClF₂ (e.g., at an elevated temperature no higher than about 400° C.). No substantial production of CClF₂ CClF₂ means herein that the molar ratio of CClF₂ CClF₂ to CCl₂ FCClF₂ in the fluorination product is less than about 1:9. Preferably, the molar ratio of CClF₂ CClF₂ to CCl₂ FCClF₂ in the fluorination product is less than about 1:19, and more preferably is less than about 1:99. The fluorination process according to the present invention can be conducted batchwise, but is preferably conducted continuously in a manner generally known to the art for conducting catalyzed vapor phase fluorination reactions.

The C₂ Cl₄ F₂ mixtures are reacted with hydrogen fluoride using a catalyst comprising trivalent chromium. In addition to a catalytically effective amount of trivalent chromium, such fluorination catalysts can include other components to increase catalyst activity and/or life such as one or more divalent metal ions (e.g., zinc, mangesium, and/or cobalt). The trivalent chromium catalyst may be unsupported (e.g., Cr₂ O₃) or supported (e.g., on alumina, aluminum fluoride, magnesium fluoride or carbon).

Suitable vapor-phase fluorination catalysts include trivalent chromium halides (e.g., CrCl₃ and/or CrF₃) supported on carbon. A preferred catalyst is CrF₃ on carbon and is disclosed in U.S. Pat. No. 3,632,834, the contents of which are incorporated herein by reference. While any suitable carbon support may be used, a preferred carbon support is acid-washed prior to depositing trivalent chromium on it. Suitable trivalent chromium catalysts may be prepared by treating the carbon used as catalyst support with an acid, preferably with two acids. Typically the support is washed with deionized water after acid treatment and dried; and the chromium halide is then deposited thereon using deposit techniques well known in the art (see e.g., Example 1 of U.S. Pat. No. 3,632,834). Preferably, the chromium content (expressed as CrCl₃) is from about 5 to 50 weight percent of the carbon-supported catalyst.

Acid treatment typically uses an acid other than hydrofluoric acid. Preferred acids used for the acid treatment contain neither phosphorus nor sulfur. Examples of acids which may be used in the first acid wash during the catalyst preparation process include organic acids such as acetic acid and inorganic acids, such as HCl or HNO₃. Preferably hydrochloric acid or nitric acid is used. The second acid treatment, when employed, advantageously uses hydrofluoric acid. Normally, the carbon is treated with acid such that after such treatment the carbon contains less than about 0.1% by weight ash.

Commercially available carbons which may be treated with acids to provide suitable supports include those sold under the following trademarks: Darco™, Nuchar™, Columbia SBV™, Columbia MBV™, Columbia MBQ™, Columbia JXC™, Columbia CXC™, Calgon PCB™, Norit™ and Barnaby Cheny NB™. The carbon support can be in the form of powder, granules, extrudates, or pellets, etc.

The acid treatment may be accomplished in several ways. A suitable procedure is as follows. A carbon support is soaked overnight with gentle stirring in a 1 molar solution of the acid prepared in deionized water. The carbon support is then separated and washed with deionized water until the pH of the washings is about 3. Preferably, the carbon support is then soaked again with gentle stirring in a 1 molar solution of the acid prepared in deionized water for 12 to 24 hours. The carbon support is then finally washed with deionized water until the washings are substantially free of the anion of the acid (e.g., Cl⁻ or NO₃ ⁻), when tested by standard procedures. The carbon support is then separated and dried at about 120° C. The washed carbon is then soaked, if necessary, in 1 molar HF prepared in deionized water for about 48 hours at room temperature with occasional stirring. The carbon support is separated and washed repeatedly with deionized water until the pH of the washings is greater than 4. The carbon support is then dried followed by calcination at about 300° C. for about 3 hours in air prior to its use as a support. Reference is made to U.S. Pat. No. 5,136,113 for further details relating to producing acid-washed carbon catalysts.

For continous processes, the fluorination is generally conducted in the reaction zone for the fluorination. The reaction zone may contain more than one reactor, multiple feed lines, as well as interstage cooling or heating, addition of reactants, diluents, recycle streams, etc. For example, multiple reactors may be used to stage the degree of fluorination so that undue temperature rise and overfluorination are avoided. The reaction product is normally recovered at the end of the reaction zone. If necessary, the reaction products, intermediates and/or by-products can be removed at various stages of the reaction zone and if desired recycled to different parts of the reaction zone. For example, HF and C₂ Cl₄ F₂ can be fed to a reaction zone at more than one feed location. CCl₂ FCClF₂ (CFC-113), is generally recovered from the end of the reaction zone.

Suitable fluorination reaction temperatures are normally from about 250° C. to 400° C. A preferred temperature range is from 275° C. to 375° C., with temperatures ranging from 300° C. to 350° C. being particularly preferred. The HF to C₂ Cl₄ F₂ ratio is normally from 0.2:1 to 4:1, and preferably ranges from 0.25:1 to 2:1. Pressure is not critical. Atmospheric and superatmospheric pressures (e.g., from about 100 kPa to about 7000 kPa) are the most convenient and are therefore preferred. The above reaction variables together with the catalyst loading are balanced one against the other such that in the fluorination products there is a molar ratio of CClF₂ CClF₂ to CCl₂ FCClF₂ in the product mixture which is less than about 1:9. One skilled in the art will recognize that higher temperatures and higher HF:C₂ Cl₄ F₂ ratios favor a higher degree of fluorination. The amount of overfluorination can thus be reduced by providing a lower HF:C₂ Cl₄ F₂ ratio and/or lower temperature. Catalyst contact time can also be adjusted in a conventional manner to control fluorination.

The product mixture from fluorination normally contains a mixture of C₂ Cl₃ F₃ (almost exclusively CCl₂ FCClF₂) small amounts of CClF₂ CF₃ (CFC-115), CClF₂ CClF₂, CCl₂ FCF₃ (CFC-114a), unreacted C₂ Cl₄ F₂ isomers and HF and HCl. The fluorination product is separated such that a portion of the C₂ Cl₃ F₃ (and any C₂ Cl₂ F₄) in the product mixture is separated from C₂ Cl₄ F₂ therein. Typically, conventional separation using one or more distillation column(s) is employed. The separation may also include one or more decanter(s). During separation by distillation, the lower boiling materials (e.g., HF, HCl, CFC-115) are separated from the CFC-112 isomers. It is noted that azeotropes of HF with various halocarbons such as CCl₂ FCCl₂ F, CCl₃ CClF₂, CCl₃ CF₃, and CCl₂ FCF₃ can form during distillation.

The CFC-112 isomers from the fluorination product (which are normally enriched in CFC-112 as a result of selective fluorination of CFC-112a) and a portion of the CFC-113 isomer from the fluorination product are fed along with additional CFC-112 to an isomerization zone, where the CFC-112 is substantially converted to CFC-112a. HF should be removed from the C₂ Cl₄ F₂ prior to contact with the isomerization catalyst. The C₂ Cl₃ F₃ present in the mixture of C₂ Cl₃ F₃ and C₂ Cl₄ F₂ fed to the isomerizer provides a melting point below the melting point of CCl₂ FCCl₂ F, thereby facilitating the desired isomerization. Preferably, the C₂ Cl₄ F₂ content is between about 10 mole percent and 75 mole percent of the C₂ Cl_(4-x) F_(2+x) fed to the isomerization step; and more preferably the C₂ Cl₄ F₂ content is between about 10 mole percent and 50 mole percent thereof. The CFC-112 is isomerized to CFC-112a in the presence of recycled C₂ Cl₃ F₃ using an aluminum chloride catalyst as disclosed in Example IV of U.S. Pat. No. 2,598,411. Isomerization of recycled CCl₂ FCClF₂ may be accomplished in the same isomerization reactor as used for the isomerization of CFC-112 to CFC-112a. However, in accordance with this invention, the molar ratio of C₂ Cl₄ F₂ to C₂ Cl₃ F₃ fed to the isomerization zone is at least about 1:9. The molar ratio of (CCl₂ FCClF₂ +CCl₂ FCCl₂ F) to (CCl₃ CF₃ +CCl₃ CClF₂) in the compounds fed to the isomerization generally at least about 1:9. Many aluminum trihalide catalysts can be employed. A preferred catalyst is an anhydrous aluminum trichloride which has been micropulverized (i.e., mechanically comminuted by crushing, ball milling, rod milling, grinding or the like) to provide a surface area of greater than about 0.8 m² /g and has been activated by treatment under agitation with at least about 10 g CCl₂ FCClF₂ per gram of aluminum trichloride. Reference is made to copending U.S. patent application Ser. No. 08/117,379 for further disclosure of micropulverized catalysts. The CFC-112a is recycled in accordance with this invention to the fluorination step.

The CFC-113 recovered from the separation zone also may be isomerized to CFC-113a using the aluminum chloride catalyst as disclosed in Example I of U.S. Pat. No. 2,598,411. As above, preferred catalysts include an activated micropulverized anhydrous aluminum trichloride with a surface area of greater than about 0.8 m² /g.

The CFC-113a from the isomerization zone can readily be reacted with HF in a reaction zone to afford high purity CFC-114a. The latter compound can then be converted by hydrogenolysis to CH₂ FCF₃ (HFC-134a), a non-ozone depleting refrigerant.

Employment of the instant invention is further illustrated by reference to FIG. 1 wherein a mixture of C₂ Cl₄ F₂ isomers containing substantial CFC-112 and optionally C₂ Cl₃ F₃ isomers containing substantial CFC-113 (i.e., the ratio of CFF-113 to CFC-113a is greater than 100:1) is fed through line (211) to an isomerizer (210). The isomerizer effluent consisting of a mixture of C₂ Cl₄ F₂ isomers containing predominantly CFC-112a and optionally C₂ Cl₃ F₃ isomers containing predominantly CFC-113a is fed through line (212) to a fluorination reactor (220). HF is fed to reactor (220) through line (221). The fluorination reactor effluent containing unreacted CCl₂ FCClF₂, unreacted C₂ Cl₄ F₂, HF and HCl and optionally C₂ Cl₂ F₄ isomers containing predominantly CCl₂ FCF₃ is fed through line (222) to a distillation column (230). A mixture of C₂ Cl₃ F₃ isomers, HF and HCl and optionally C₂ Cl₂ F₄ isomers is collected at the top of the column and recovered through line (232). A mixture of C₂ Cl₄ F₂ isomers enriched in CFC-112 and C₂ Cl₃ F₃ enriched in CFC-113, from the bottom of column (230), is fed through line (231) back to the isomerizer (210) along with additional CFC-112 through line (213).

The reactors and their associated feed lines, effluent lines and associated units should be constructed of materials resistant to hydrogen fluoride, hydrogen chloride and chlorine. Typical materials of construction, well-known to the fluorination art, include stainless steels, in particular of the austenitic type, and the well-known high nickel alloys, such as Monel® nickel-copper alloys, Hastelloy® nickel-based alloys and, Inconel® nickel-chromium alloys. Also suitable for reactor fabrication are such polymeric plastics as polytrifluorochloroethylene and polytetrafluoroethylene, generally used as linings.

Practice of the invention will become further apparent from the following non-limiting examples.

EXAMPLES

General Reaction Procedure

A 5/8" (1.58 cm) I.D. Inconel® nickel alloy reactor was charged with a catalyst and heated to 300° C. in a flow of nitrogen (25 mL/min) for about 20 hours. The temperature was reduced to 175° C. and a 2:1 molar ratio of nitrogen and HF was started through the reactor (total flow 100 mL/min). After one hour under these conditions, the molar ratio of nitrogen to HF was adjusted to 1:3 and the temperature increased gradually over a two hour period to 400° C. The reactor was then brought to the desired operating temperature, the nitrogen flow stopped, and the flow of reactants started.

General Analytical Procedure

The reactor effluent was sampled on-line with a Hewlett Packard HP 5890 gas chromatograph using a 20 foot (6.1 m) long, one-eighth inch (0.32 cm) diameter, column containing Krytox™ perfluorinated polyether on an inert support and a helium flow of 35 mL/min. Gas chromatographic conditions were 70° C. for three minutes followed by temperature programming to 180° C. at a rate of 6° C./minute. The table percentages are in mole %.

EXAMPLE 1 Fluorination of CCl₂ FCCl₂ F/CCl₂ FCClF₂ Mixtures

The General Reaction Procedure was followed using a 29% CrCl₃ on carbon catalyst (10.8 g, 25 mL), a molar composition of chlorofluorocarbons (CFCs) containing CCl₂ FCCl₂ F (64.7%), CCl₂ FCClF₂ (35.1%), and CCl₃ CF₃ (0.2%), an HF:CFCs molar ratio of 2:1 and a contact time of 30 seconds. The reaction was run at atmospheric pressure. The results at various temperatures are shown in Table 1.

                  TABLE 1                                                          ______________________________________                                         Temp.                                                                          (°C.)                                                                         115.sup.(a)                                                                            114.sup.(b)                                                                            114a.sup.(c)                                                                          113.sup.(d)                                                                          113a.sup.(e)                                                                          112/a.sup.(f)                        ______________________________________                                         325   0.2     1.6     1.3    55.1  0.2    41.0                                 350   0.4     4.6     1.9    69.3  0.3    22.7                                 375   0.9     9.7     3.6    73.7  0.4    10.3                                 ______________________________________                                          .sup.(a) 115 is CClF.sub.2 CF.sub.3 -                                          .sup.(b) 114 is CClF.sub.2 CClF.sub.2 -                                        .sup.(c) 114a is CCl.sub.2 FCF.sub.3 -                                         .sup.(d) 113 is CCl.sub.2 FCClF.sub.2 -                                        .sup.(e) 113a is CCl.sub.3 CF.sub.3 -                                          .sup.(f) 112/a is CCl.sub.2 FCCl.sub.2 F + CCl.sub.3 CClF.sub.2 (The           isomers of C.sub.2 Cl.sub.4 F.sub.2 cannot be distinguished using the          above analytical method. In this example it is believed that the product       consists essentially of CCl.sub.2 FCCl.sub.2 F).                         

Other products identified include CF₃ CF₃, CCl₂ ═CClF, CCl₃ CCl₂ F and CCl₂ ═CCl₂.

EXAMPLE 2 Fluorination of CCl₃ CClF₂ /CCl₂ FCClF₂ Mixtures

The General Reaction Procedure was followed using a 29% CrCl₃ on carbon catalyst (10.8 g, 25 mL), a molar composition of chlorofluorocarbons (CFCs) containing CCl₃ CClF₂ (63.8%), CCl₂ FCClF₂ (35.8%), and CCl₃ CF₃ (0.2%), an HF:CFCs molar ratio of 2:1 and a contact time of 30 seconds. The reaction-was run at atmospheric pressure. The results at various temeperatures are shown in Table 2.

                  TABLE 2                                                          ______________________________________                                         Temp.                                                                          (°C.)                                                                           115    114      114a 113    113a 112/a.sup.(a)                         ______________________________________                                         300     0.1    0.9      0.7  90.9   0.5  6.2                                   325     0.1    3.2      1.6  90.1   0.4  3.9                                   350     0.3    6.0      2.1  86.9   0.4  3.9                                   ______________________________________                                          112/a is CCl.sub.2 FCCl.sub.2 F + CCl.sub.3 CClF.sub.2 (The isomers of         C.sub.2 Cl.sub.4 F.sub.2 cannot be distinguished using the above               analytical method. In this example it is believed that the product             consisted essentially of CCl.sub.3 CClF.sub.2).                          

Other products identified include CCl₂ ═CClF and CCl₂ ═CCl₂.

Particular embodiments of the invention are illustrated in the Examples. Other embodiments will become apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is understood that modifications and variations may be practiced without departing from the spirit and scope of the novel concepts of this invention. It is further understood that the invention is not confined to the particular formulations and examples herein illustrated, but it embraces such modified forms thereof as come within the scope of the claims which follow. 

I claim:
 1. A process for producing a reaction product comprising C₂ Cl₃ F₃ substantially free of CClF₂ CClF₂, comprising the steps of:(i) contacting a feed mixture consisting essentially of compounds of the formula C₂ Cl_(4-x) F_(2+x) wherein x is 0 or 1 wherein the C₂ Cl₄ F₂ content is between about 10 mole percent and 90 mole percent of said C₂ Cl_(4-x) F_(2+x) and wherein the mole ratio of the total amount of CCl₂ FCCl₂ F and CCl₂ FCClF₂ to the total amount of CCl₃ CClF₂ and CCl₃ CF₃ is at least about 1:9, with an isomerization catalyst to produce isomerization product wherein there is less than about 50,000 parts by weight total CCl₂ FCCl₂ F and CCl₂ FCClF₂ per million parts by weight total of CCl₃ CClF₂ and CCl₃ CF₃ ; (ii) contacting the isomerization product with HF in the vapor phase in the presence of a fluorination catalyst comprising trivalent chromium at an elevated temperature below 400° C. selected to provide a fluorination product containing C₂ Cl₂ F₄, C₂ Cl₃ F₃ and between about 10 and 90 percent of the C₂ Cl₄ F₂ from the isomerization product, wherein the ratio of CCl₂ FCCl₂ F to CCl₃ CClF₂ and the ratio of CCl₂ FCClF₂ to CCl₃ CF₂ are both greater than the ratios thereof in the isomerization product and wherein the molar ratio of CClF₂ CClF₂ to CCl₂ FCClF₂ is less than about 1:9; (iii) recovering the C₂ Cl₂ F₄ and a first portion of the C₂ Cl₃ F₃ from the fluorination product; and (iv) recycling C₂ Cl₄ F₂ and a second portion of the C₂ Cl₃ F₃ from the fluorination product to step (i) along with an additional amount of CCl₂ FCCl₂ F which is at least equal to the amount of C₂ Cl₂ F₄ and C₂ Cl₃ F₃ recovered in step (iii) and is sufficient to provide said feed mixture ratio of C₂ Cl₄ F₂ to C₂ Cl_(4-x) F_(2+x).
 2. The process of claim 1 wherein the fluorination catalyst comprises trivalent chromium supported on acid-washed carbon.
 3. The process of claim 2 wherein the fluorination catalyst is a chromium halide supported on acid-washed carbon.
 4. The process of claim 3 wherein the chromium content of the catalyst is from 5 to 50 weight percent expressed as CrCl₃.
 5. The process of claim 1 wherein the C₂ Cl₄ F₂ content of the feed mixture is between about 10 mole percent and 75 mole percent of the C₂ Cl_(4-x) F_(2+x) therein.
 6. The process of claim 1 wherein the C₂ Cl₄ F₂ content of the feed mixture is between about 10 mole percent and 50 mole percent of the C₂ Cl_(4-x) F_(2+x) therein.
 7. The process of claim 1 wherein the fluorination reaction temperature is from about 250° C. to 350° C.
 8. The process of claim 1 wherein the HF:C₂ Cl₄ F₂ ratio for the fluorination step is from 0.2:1 to 4:1.
 9. The process of claim 1 wherein the molar ratio of CClF₂ CClF₂ to CCl₂ FCClF₂ in the fluorination product is less than about 1:19.
 10. The process of claim 1 wherein the molar ratio of CClF₂ CClF₂ to CCl₂ FCClF₂ in the fluorination product is less than about 1:99. 